During the last wash, I got water into one of the two amps for my empeg. I opened the case after it kept blowing the external 30A fuse. I found two parts to be shorted which look like voltage regulators (but I don't know what they are). They are three-legged parts with a plastic body, with a hole on the metal back that extends over the body (I can attach pics, if necessary). There is a whole bunch of these in my amp, so it was easy to find out, which ones were faulty by measuring resistance across the pins. I removed the ones that had zero resistance across the two outer pins.
The three lines of characters on the plastic bodies of the two parts read as follows:

IRF 540
I<unrecogn. char>R 115E
30 18

What part is that? I do have some voltage regulators lying around here from Patrick's tuner kits (had to replace some there, because of a power supply that was set too high), but the text on them doesn't match.

Thanks for any help!

That appears to be an output transistor (ie one end goes out to the speaker terminal) There are typically multiple of these running in parallell, as a single one couldn't handle the current required and/or the power dissipation (heat losses).

A google gives a lot of sources, for instance www.mouser.com

Edit:
Could also be used for other purposes, but if it was attached to the heat sinks then it's most likely used as an output transistor.

In Germany I think Conrad would be a place that would have them.

/Michael

I assume they're this:
http://www.semiconductors.philips.com/pip/IRF540.html

(power transistors)

And in quantity 1 you can get em for $.47 per, if not less

http://buy.semiconductors.com/cgi-bin/pldb/shop.cgi/934055542127

Even if you do manage to replace the bad transistors, there's no guarantee your amp will work. It's possible that they failed as a downstream result of some other failure.

But it can't hurt to try I suppose.

Yup, they're on the heatsink alright and in parallel. Thanks a lot, I'll see Conrad to get them!

Of course, there could be numerous other components fried. However, I could see where the water had gone and I couldn't find any other components to be as obviously fried as the two transistors. I'll just hope that the two transistors will fix it, but of course there's no guarantee...

N-channel enhancement mode power MOSFETs.

Pins;
1 2 3
G D S

You definitely shouldn't be seeing 0 ohms across pins 1 and 3. I'm concerned that perhaps the MOSFETs themselves aren't blown but maybe something that was in parallel with them. Can you remove one from the circuit and check the resistance across the pads? Also can you confirm the resistance between pins 1 & 2, and 2 & 3.

The gate failure mode of MOSFETs is usually static related, not heat related. The resistance between pins 1 & 3 should be in the region of 200 - 2000 Megohms. Most 'meters will just show this as infinite. Even if the gate- - drain voltage was 20V, the gate current would still be less than 100nA, (100 x 10^-9 A), ie not enough to do any damage.

Even if I take the transistors out, they show 0 ohms accross pins 1 and 3...

If I check the pads, they now show the same 550 ohms (I think, don't have it here) without the defective transistors, that I measure across the other transistors.

I'll check the resistance between the pins 1&2 and 2&3 tonight and will post it then.

I could see water stains (must've been water with shampoo or something, really thick!) across the pins (underside) and would assume salt-bridges forming and bypassing the current to cause the transistors to fry. I have some more components that were covered in the stains, but they either seem to do fine, or I didn't know how to measure them (diodes?) without an external power supply. If it's not working after I replaced the transistors, I'll take it here to work with me, where I have the power-supplies I need (I really should get one for home, I've needed one a few times now).

Thanks for you help! I wouldn't know what to do without you guys!

OK, sounds like it is the MOSFET that is blown then.

You want the SOT78 / TO220AB part.

I'd think so too (even though this doesn't preclude something else being shot, too). I just measured across pins 2&3 and 1&2: it's 0 ohms (both combinations) for one of the two MOSFETs (i.e. 0 ohms across any two of the three pins) and 0 ohms and 15.6 ohms for the other. I think they're clearly shot. Now I just need to be lucky and they're the only thing that's fried and are not just being fried because of some other problem!
Wish me luck! I so miss my bass!

Ok, I admit I'm not much of an electronics freak (I guess you could already tell that LOL ). So I replaced the MOSFETS and tested the amp. No fuse blew with no audio input (i.e. key in ignition, empeg on, RCAs disconnected). I connected the RCAs and everything worked just beautifully, perfect sound. I bolt everything down, make sure everything is nice and tidy, start the car and the fuse blows again! I open the amp and now the same two MOSFETS but on the other channel are blown. Obviously, there's something fried that's common to both channels. But all compoents that I could visually inspect and measure with a multimeter check out fine.
Why was it running without the engine on but blew once I started the engine? Where could a difference from 12V to 14V make such a huge difference (It's a 30A fuse that keeps blowing)? When I tested the amp with the engine off, key on, I even turned the empeg all the way open and it worked just fine. Where do you think should I look with a description like this?

Where do you think should I look with a description like this?

Well, two places, I'd think: 1. Stereo shop for a new amplifier, 2. Auto parts shop for gasket sealant to close up the water leak.

LOL, very true. Problem with 1. is that I have a Miata and it took me ages to find the Memphis amp that fits so perfectly in the tunnel next to the tank (stealth install) and that amp was very expensive (i.e. justifying the amount of work I'm putting in). I'd also have a hard time finding one for sale now, since it's fairly old.
I'll definitely fix 2, though, no question.